PMRF Ph.D. Overview

Exploiting the anisotropic nature of composite laminates is a driving factor to improve the design regime of multistable structures. The concept of laminate tailoring is being taken a step ahead by allowing variation in fiber angle orientation within the ply planform. Such composite laminates known as variable stiffness (VS) composites have been reported to provide significant improvements in performance over constant stiffness designs. The phenomenon of snapping from one stable state to another is of paramount importance for multistable structures to be used in morphing applications. VS laminates allow the designer to tailor structural response according to the requirements of the morphing mechanism. This work presents a study to explore designs by exploiting the tailoring options in VS laminates, with the use of microfiber composites actuators.

In practice, morphing structures need to be controlled in order to maintain or achieve a desired shape. To do so, an appropriate dynamic model has to be derived. During this process, structural characteristics should be investigated by considering the interaction between dynamic characteristics and the modes of actuation. In order to address this problem, the idea of dynamically inducing snap-through in multistable structures could be proposed. Experimental investigations on the dynamic snap-through of morphing bistable straight fibre laminates reported that dynamic actuation significantly reduces the snap-through voltages by exploiting the linear and non-linear dynamic characteristics of the lamina assembly . The modified actuation strategy makes use of the dynamics of the bistable structure to achieve the change between stable shapes more efficiently by increasing the actuator’s authority to induce snap-through action in the morphing process. In this work, the concept of dynamic actuation could be exploited on both thermally and mechanically induced bistable VS laminates to further reduce the snap-through requirements.

Multistable laminates have been actively researched in the recent past, due to its potential in morphing applications in different engineering sector. Unsymmetical cross-ply laminates, which yields two cylindrical stable shapes are widely investigated multistable structures, where the multistability is induced due to the thermal residual stresses. However, to improve the design space in such laminates, VS laminates with curvilinear fiber paths have been investigated recently. They have been found to generate diverse stable shapes, with the possibility to tailor snap-through loads. Connecting two different laminate plates can generate more than two stable configurations, often desired in morphing applications. This study aims to develop a highly multistable continuous composite plate by connecting two square VS laminates without any external fixing aids. A parametric study is performed to understand the effect VS parameters on the snap-through forces in comparison to the results from conventional cross-ply laminates. The multistable shapes of the series-connected laminates are analysed within a commercially available finite element package. It is concluded from the study that VS laminates can produce multiple equilibrium states with lower actuation requirements, without compromising much on out-of-plane displacements. 

The objective of the master thesis is to develop a Finite Element model for multistable VS laminates. This would include working on commercial FE package (ABAQUS) and developing user routines to model VS composites. The FE calculations would be verified with the existing semi-analytical results, and it would be used to find out VS configurations that have low snap-through forces but high out-of-plane displacements. The tasks would include linking the semi-analytical framework build in MATHEMATICA/MATLAB with commercially available ABAQUS package to create an efficient framework for practical applications. This modeling approach would be achieved for composite plates with different geometrical conditions. The snap-through forces and the out-of-plane displacements of multistable shapes built from VS laminate and with straight fiber laminates will be compared.

The objective of the master thesis is to develop a Finite Element model for multistable VS laminates. This would include working on commercial FE package (ABAQUS) and developing user routines to model VS composites. The FE calculations would be verified with the existing semi-analytical results, and it would be used to find out VS configurations that have low snap-through forces but high out-of-plane displacements. The tasks would include linking the semi-analytical framework build in MATHEMATICA/MATLAB with commercially available ABAQUS package to create an efficient framework for practical applications. This modeling approach would be achieved for composite plates with different geometrical conditions. The snap-through forces and the out-of-plane displacements of multistable shapes built from VS laminate and with straight fiber laminates will be compared.